An Astronomical Evidence of Existence of Quark Matter and the Prediction for Submillisecond Pulsars

We derive the bulk viscous time scale of neutron stars with quark matter core, i.e. hybrid stars. The r-mode instability windows of the stars show the theoretical result accords with the rapid rotation pulsar data. The fit gives a strong indication for the existence of quark matter in the interior of neutron stars. Hybrid stars instead of neutron or strange stars may result in submillisecond pulsars if they exist.